Stable G-quadruplexes are found outside nucleosome-bound regions.

Unusual DNA structures such as four-stranded G-quadruplexes have been found to form in vivo and to play regulatory roles. However, since DNA is normally present as chromatin, with the double helix wrapped around histone proteins, it is unclear how a G-quadruplex could form in such a region. Here, we show that regulatory G-quadruplexes found upstream of transcription start sites are in fact located in a region depleted of nucleosomes, and that in general in both Caenorhabditis elegans and humans, stable G-quadruplexes are located outside nucleosome-bound regions, hence making it easier for them to form in vivo.